Plate type heat exchangers have long been popular for a variety of heat transfer applications, particularly in the vehicular field. In the usual case, a series of plates are stacked in spaced relation. The spaces between adjacent plates define flow channels for the heat transfer fluids. Typically, aligned rows of holes are disposed in the plates and through the use of separators and/or baffles, are caused to provide fluid communication to only certain of the flow channels. In a typical case, for a two fluid plate type heat exchanger, every other channel from top to bottom of the stack will receive a heating/cooling fluid while the channels at the interface between the heating/coolant channels receives the fluid to be subject to the heat transfer operation. In typical vehicular applications, the heating/coolant fluid is typically engine coolant while the fluid being subject to the heat transfer operation will typically be some sort of oil as, for example, engine lubricating oil, transmission oil, oil used in other hydraulic systems, or retarder oil.
As vehicles become more and more complex, there is an increasing need to provide for cooling of the oil of each of the many vehicular systems that employs oil. Plate heat exchangers of the type described previously have only two separate circuits, one for the coolant and one for the oil. Consequently, in a vehicle having several sources of oil requiring cooling, it is necessary to employ a separate heat exchanger for each source of oil. This, of course, adds to the complexity of the fluid system of the vehicle and furthermore adds weight, which impacts on fuel economy. Furthermore, each separate heat exchanger adds to the cost of the heat exchange system. Moreover, the use of several heat exchangers in such a situation requires a greater space within the vehicle to house the heat exchangers.
In an attempt to alleviate the problem is disclosed in WO document 95/35474. According to this disclosure, three separate circuits for three different fluids are integrated into a single heat exchanger. In an especially preferred embodiment of such a heat exchanger, only two differently formed heat exchanger plates are required. These are inserted into one another in a certain way and forms three separate flow channels. However, they must be rotated by 180 degrees and failure to do so will result in a defective heat exchanger. Furthermore, all of the heat exchanger plates have a total of six openings for the passage of fluids. As a result of such a large number of openings, the potential for leakage at joints is increased.
The present invention is directed to overcoming one or more of the above problems.